This study will develop a new weight-for-height index which adjusts for the age of the child. Relative weight indices such as Quetelet and Ponderal indices that have been used on adult populations do not work well for children. They tend to be strongly correlated with age and are not predictive of body fat. Polynomial regression models that include age terms were fitted to weight and height data for children between the ages of 3 to 12 years from the National Health and Nutrition Examination Survey II in order to estimate a standardized weight-for-height which is adjusted for the age of the child. Separate regression models were estimated for boys and girls. A relative weight index was established using the estimated standard weights from the regressions. This relative weight index was compared to triceps and subscapular skinfold measurements. The new relative weight index had the desirable properties of being uncorrelated with age and highly associated with skinfold measurements. The derived relative weight index can be used in the analysis of epidemiologic studies that require an easily calculated index of obesity among prepuberty children.